This study showed that in hippocampal slice one can find evidence that hilar mossy cells have an excitatory effect on granule cells. The methods used field recordings and voltage-sensitive dye imaging. This study was important because most anatomical data suggest that mossy cells only innervate granule cells that are far from te cell body of the mossy cell. They also show that at the population level, one can detect the excitatory effect of mossy cells on granule cells.